Defect Engineering: Synthesis and Electrochemical Properties of Two-Dimensional Mo_1.74CT MXene

The creation of vacancies and/or pores into two-dimensional materials, like graphene and MXenes, has shown to increase their performance for sustainable applications. However, a simple and affordable method with controlled and tailorable vacancy concentration and/or pores size remains challenging. Herein, a simple and reproducible method is presented for controlled synthesis of Mo_1.74CT MXene with randomly distributed vacancies and pores, obtained from selective etching of both Ga and Cr in the Cr-alloyed MAX-phase like precursor Mo_1.74Cr_0.26Ga₂C. Structural and compositional analysis of the 3D alloy show ≈13% Cr on the metal site, homogeneously distributed between different particles and within the atomic structure. After etching, it translates to Mo_1.74CT MXene, exhibiting defect-rich sheets. Notably, the incorporation of Cr facilitates a shorter etching time with an improved yield compared to Mo₂CT . The Mo_1.74CT MXene displays excellent electrochemical properties, almost doubling the capacitance values (1152 F cm^-3 and 297 F g^-1 at 2 mV s^-1 scan rate), compared to its pristine counterpart Mo₂CT . The presented method and obtained results suggest defect engineering of MXenes through precursor alloying as a pathway that can be generalized to other phases, to further improve their properties for various applications.